Kelly is out indefinitely. The severity of the break is unknown. The Bruins have not said whether he will require surgery.

Kelly, 32, was hurt when he collided with former Senators teammate Chris Neil. The Ottawa bruiser banged his left knee into Kelly’s leg. Neil said it was an accident, a sentiment shared by Bruins coach Claude Julien.

Kelly traveled with the Bruins to Pittsburgh Monday; at the time, the team had not determined the nature of the injury because of swelling.

In eight NHL seasons, Kelly has missed only 10 games because of injury. This year, he has 2 goals and 4 assists in 23 games. Kelly has been the No. 3 center and one of six regular penalty-killing forwards.

The Bruins have not recalled a center from Providence. On Tuesday against Pittsburgh, Rich Peverley replaced Kelly as the third-line center.

Peverley is a natural center who is comfortable taking faceoffs and killing penalties, two of Kelly’s assets. The Bruins are carrying one extra forward in Lane MacDermid.

The Bruins had been seeking a third-line upgrade prior to Kelly’s injury. They are hoping to land Carl Soderberg following the forward’s playoff run with Linkoping of the Swedish Elite League. They could also look for help via the trade market.